Recording system



Jan. 13, 1.942'. R, R, scovllrLE 2,2695638 4 REGORMNG SYSTEM FiledNOv. 15,1958

F/G. Y l//\ SVS NOISE 2 REaucTlo/v NETWORK FIG. 2 FIG. 3 M *IP-.C w /o 1 /J "2 6V V`s" Y 5"- 'gf-"11| l L I L, F f1 ulllll VB-4 f N A 26 TTRA/EV Patented Jai.. 13, 1942 RECORDING SYSTEM Ray R. Scoville, kLos Angeles, Calif., assignor to Electrical Research Products, Inc., New York, N. Y., a corporation of Delaware Application November 15, 1938, Serial No. 240,502

7 Claims.

` invention relates to film sound recording systems and particularly to improvements in such systems employed to record two complete complementary records of the sound waves in one sound track.

The object of the invention is to provide a method and apparatus for recording a negative photographic sound record in the form of an exposed` area laterally displaced in accordance with the variations of sound currents, the lateral width of the sound area varying in accordance with the envelope of the amplitude variations of the sound currents.

A feature of the invention lies in the provision of a sound recording system employing a single modulating device including a pair of spaced, opaque elements disposed in the recording light beam to define the vertical marginal edges thereof and so connected to the sound source that they vibrate laterally in parallel relation in response to sound currents but laterally in opposite directions in response to biasing noise reduction currents.

Sound recording systems for producing photographic sound records having an exposed area laterally displaced in accordance with variations in sound currents and having the lateral width of the exposed area varying in accordance with the envelope of the amplitude variations of the sound currents, are known. In recording systems developed heretofore for recording this type sound record, two separate light modulating devices have been required, one to control the width of the light beam in accordance with the envelope of the amplitude variations of the sound gz ducting elements immersed in the constant magfr netic field of a single modulating unit and an image of one edge of each of the opaque elements is formed at the plane of the recording film. The opaque conducting elements are connected to a source of sound currents and to a source of biasing noise reduction currents in a novel manner to produce passage of the sound currents through the elements in the same direction and passage of the biasing noise reduction currents through the elements in opposite directions. The magnetic fleld'produced by the sound currents flowing in the opaque members react with the constant magnetic eld to produce lateral movement of the elements in the same direction, resulting in a shift of the light beam v defined by the elements laterally of the lm.

The magnetic field produced by the biasing noise reduction currents flowing in the separate conducting elements in opposite directions reacts with the constant magnetic field to produce lateral movement of the elements in opposite directions to vary the width of the light beam during lateral movement thereof in response to sound currents.

In the negative record produced by the recording system in accordance with the invention the central exposed area will be as small as possible so that on a positive release print made therefrom, the transparent area will be as small as possible to insure a minimum of ground noise. Fig. 1 is a diagrammaticl representation of a sound recording system embodying this invention; Fig. 2 is a fragmentary enlarged view of a ligh valve showing the adjusted position of the conducting -elements with respect to the light denning aperture in accordance With this invention; Fig. 3 is an enlarged showing of a negative `251m sound record produced by the recording sysi tem of Fig. 1; and

Fig. 4 is an enlarged showing of a positive film 'record obtained from the negative record shown in Fig. 3.

In Fig. 1, the modulating device in accordance with the invention comprises a pair of opaque, current conducting ribbons I and 2 immersed in the constant magnetic eld of permanent magnets 3 and 4. The conducting elements, or ribbons, I and 2 are disposed at right angles to an aperture 5 in pole-piece member 6. The aperture 5 is preferably rectangular in shape, having its longer axis disposed transverse to the longitudinal axis of the recording film.

The modulating device or light valve disclosed in Fig. 1 may be structurally similar to the light valve shown in U. S. Patent 1,914,186, patented June 13, 1933, to E. C. Wente, except that the opaque conducting elements or ribbons in the light valve herein disclosed are disposed parallel to the longitudinal axis of the sound record. Suitable Well-known means may be provided for tensioning and space adjusting the conducting ribbons I and 2 and for clamping these ribbons in adjusted position with respect to aperture 5.

Light from a source 'I is focussed by a lens system 8 on the aperture 5. Light transmitted through the aperture 5 is focussed, by means of a lens system 9, on the record track area I of a photographic lm F. The lm F is moved through the recording light beam at a continuous, uniform speed by suitable film driving apparatus.

A pair of elements II and I2, having equal impedances, are included in a balanced bridge circuit with conducting elements I and 2.

A microphone I3 is disposed in the vicinity of the source of sound to be recorded. The modulated signal wave from the microphone I3 is amplied in amplier I4 and supplied to the primary of transformer I5. One terminal of the secondary of transformer I5 is connected by lead I6 to junction I'I of the two current responsive ribbons I and 2. The other terminal of the transformer secondary is connected by lead I8 to junction I9 of the two impedance elements II and I2.

The portion of the modulated currents from the amplier I4 is supplied, through lead 20, to a noise reduction network 2|. This noise reduction network produces at its output terminals a current varying in accordance with the envelope of the amplitude variations of the modulated signal current. A noise reduction network suitable for use in the recording system described herein is disclosed in U. S. Patent 2,077,193, patented April 13, 1933, to E. C. Wente, wherein, in the absence of signal currents, a constant source of current is supplied to the current responsive ribbons I and 2 to draw them close together.

One output terminal of the noise reduction network 2I is connected through the lead 22 to junction 23 of ribbon I and impedance elerment I I. A second output terminal of the noise reduction network 2| is connected through lead 24 to junction 25 of ribbon 2 and impedance element I2.

In Fig. 2 the current responsive ribbons I and 2 are shown in the position of proper adjustment with respect to aperture 5 before operation. As shown in this figure, the ribbons are space adjusted so that each ribbon covers one-fourth of the length of the aperture from opposite marginal edges thereof. When the light valve is adjusted in the optical recording system of Fig. 1 prior to operation thereof by the sound currents, an image of substantially one-half of each of the ribbons is formed upon the sound track I0 of the film F, each image occupying one-fourth of the lateral width of the sound track from opposite marginal edges thereof.

After the electrical connections to the light valve are made and prior to the recording operation, a constant source of current from the noise reduction network causes the ribbons I and 2 to draw very close together, leaving a narrow opening between them as indicated at C in Fig. 3. When signal currents are supplied to the noise reduction network 2|, the rectified current produced overcomes the effect of the constant current and permits the ribbons I and 2 to move away from each other, for example, to a distance indicated at D in Fig. 3, so that the image of the working edge of each ribbon will oscillate in response to the signal current without passing beyond the center line of the lm sound track. The recording system is so adjusted that for maximum amplitude sounds to be recorded, noise reduction current will produce separation of the ribbons I and 2 to the position shown in Fig. 2 so that the image of the working edge of each ribbon will oscillate within one-half the width of the film sound track to produce a record as shown within the lm section E in Fig. 2.

In Fig, 2, the arrows S indicate the direction of flow of the signal modulated currents while arrows B indicate the direction of flow of the biasing noise reduction currents in the ribbons I and 2 when connected in the recording system of Fig. l.

Fig. 3 is an enlarged representation of a developed negative sound track produced by the recording system of Fig. 1. The exposed area 26 is laterally displaced in sound track area I0 in accordance with the signal modulated currents and the width of this laterally displaced area varies in accordance with the envelope oi the amplitude variations in the signal currents.

Fig. 4 is an enlarged representation of a positive record obtained from the negative record of Fig. 3. The transparent area 21 on each side of the sound track center line is a complete photographic record of the recorded sounds, the record on one side of the sound track center line being degrees out of phase with the record on the other side of the sound track center line.

The positive sound record shown in Fig. 4 is known to those skilled in the art as a push-pull sound record and may be reproduced by separate light sensitive elements included in any well-known push-pull electrical reproducing circuit.

What is claimed is:

1. In a sound recording system including means for producing a rectangular beam of light, a light valve including a pair of spaced parallel conducting ribbons for defining the vertical edges of said rectangular beam of light, means for forming an image 0f said ribbons on a film, means for vibrating said ribbons laterally in parallel relation in accordance with the sounds to be recorded, and means for laterally vibrating said ribbons in opposite directions in accordance with the envelope of the amplitude variations of the sound to be recorded.

2. The method of recording modulated electric current upon a photographic lm which comprises projecting a narrow beam of light upon a pair of spaced opaque elements, forming an image of one edge of each of said elements on said film, laterally oscillating sald images in parallel relation by and in accordance with the variations in said current, and laterally displacing said images in opposite directions in accordance with the envelope of the amplitude variations in said current.

3. The method of recording a modulated electric current upon a photographic lm which comprises projecting a narrow beam of light having its longer axis transverse to the longitudinal axis of the film upon a pair of spaced opaque elements having their axes aligned with the longitudinal axis of the lm, forming an image of one-half of each of said elements upon the film, each image occupying one-quarter of the lateral width of the sound track from opposite marginal edges thereof, laterally oscillating said elements in parallel relation in accordance with the modulated electric current, and laterally displacing said elements toward and away from each other in accordance with the envelope of the amplitude variations of the modulated electric current.

4. In a sound recording system, a source of light, a light sensitive medium moved at constant speed, a source of sound modulated currents, a source of currents modulated in accordance with the envelope of the amplitude variations of the modulated currents, alight valve disposed in said recording system to control the light from said source impressed on said medium, said valve including a pair of flat, conducting ribbons irnmersedin a constant magnetic eld and stretched in parallel relationship to dene opposite parallel sides of a narrow, rectangular light transmitting slit, means for supplying current from said first-mentioned source of currents to both said ribbons to cause said modulated currents to ow in said ribbons in the same direction, and means for supplying currents from said second-mentioned source of currents to both said ribbons to cause said modulated currents to flow in said ribbons in opposite directions.

5. In a system for recording modulated electric currents in combination, an optical system including a source of light, a photographic lm moved at constant speed, a rectangular apertured opaque member disposed in said optical system with the longer axis of the aperture transverse to the longitudinal axis of said lm, a lens system for focussing light from said source onto said aperture, a pair of spaced opaque parallel conducting ribbons having their longer axes parallel to the longitudinal axis of said lm and defining opposite ends of the light beam projected through the aperture in said opaque member, means for producing a constant magnetic eld in which said apertured member and said ribbons are immersed, a source of modulated electric current, means for supplying current from said source to said ribbons to cause said ribbons to oscillate laterally in the same direction to produce lateral oscillation of the light beam defined thereby, a source of currents varying in accordance with the envelope of the amplitude variations of the modulated electric currents, means for supplying current from said source to said ribbons to cause said ribbons to oscillate laterally in opposite directions to vary the Width of the light beam defined thereby and a lens system for forming an image of said aperture and one edge of each of said ribbons upon said film.

6. In a sound recording system, a source of light, a light sensitive medium moved at constant speed, a source of sound modulated currents, a source of currents modulated in accordance with the envelope ofthe amplitude variations of the modulated currents, a pair of conducting ribbons immersed in a constant magnetic eld and stretched in parallel relationship to dene opposite parallel sides of a narrow, rectangular light transmitting slit, a balanced bridge circuit including said pair of conducting ribbons and two equal resistance elements, electrical connections from said source of modulated currents to one diagonal of said bridge circuit, and electrical connections to the other diagonal of said bridge circuit from said second-mentioned source of current.

7. In a sound recording system, a source of light, a light sensitive medium moved at constant speed, a source of sound modulated currents, a source of currents modulated in accordance with the envelope of the amplitude variations of the modulated currents. a pair of conducting ribbons immersed in a constant magnetic iield and stretched in parallel relationship to deiine opposite parallel sides of a narrow, rectangular light transmitting slit, a balanced bridge circuit including said pair of conducting ribbons and two equal resistance elements, electrical connections from said rst-mentioned source of currents to the common junction of said ribbons and the common junction of said resistances, and a connection from each terminal of said second-mentioned source of current to a junction of one of said ribbons and one of said resistances- RAY R. SCOVILLE. 

